During the lifetime of a patient, it may be necessary to perform a total shoulder replacement procedure on the patient as a result of, for example, disease or trauma. In a total shoulder replacement procedure, a humeral component having a head portion is utilized to replace the natural head portion of the arm bone or humerus. The humeral component may include an elongated intramedullary stem which is utilized to secure the humeral component to the patient's humerus. In such a total shoulder replacement procedure, the natural glenoid surface of the scapula is resurfaced or otherwise replaced with a glenoid component that provides a bearing surface for the head portion of the humeral component. The humeral component may be made without a stem or with a short stem.
As alluded to above, the need for a shoulder replacement procedure may be created by the presence of any one of a number of conditions. One such condition is the deterioration of the patient's scapula in the glenoid surface as a result of, for example, glenohumeral arthritis. In such a condition, erosion of the patient's scapula may be observed. The erosion may be asymmetric, anterior or posterior. Posterior erosion of on the glenoid surface is particularly common. Such erosion of the scapula renders treatment difficult, if not impossible, with a conventional glenoid prosthesis.
In order to treat a condition in which a portion of the scapula has been eroded, a number of glenoid prostheses have heretofore been designed. Such glenoid prostheses, known generally as augmented glenoid prostheses, have a posterior edge that is thicker than the corresponding anterior edge.
In FIG. 1, a heretofore-designed augmented glenoid component 1 is shown. The glenoid component 1 has a metallic backing component 5 and plastic insert 4.
The thickness of the metallic backing component 5 gradually increases from an anterior edge to a posterior edge thereof. The arcuate-shaped medial surface 2 may over time lead to loosening of the augmented glenoid component 1, thereby potentially necessitating additional surgical procedures to replace or reseat the component 1. Further, due to the configuration of the medial surface 2, a relatively high shear load is created along the implant-to-bone interface when the component 1 is implanted. The presence of a high shear load along the implant-to-bone interface tends to also cause loosening of the component 1 over a period of time. Post-operative loosening is the largest cause of failures of implanted glenoid components.
As shown in FIG. 1, the metal backing may include additional features in the form of, for example, pegs 6 and center peg 7 to provide additional support of the glenoid implant on the scapula 3.
In FIG. 2 another heretofore-designed augmented glenoid component 8 is shown. The glenoid component 8 has a single component plastic body 9A. The thickness of the plastic body 9A gradually increases from an anterior edge 8A to a posterior edge 8B thereof thereby creating a relatively smooth, arcuate-shaped medial surface 10 from which a number of posts or pegs 8 extend. The design of this augmented glenoid component 8, however, suffers from at least the same drawbacks as the glenoid component 1.
In FIG. 3 another heretofore-designed augmented glenoid component 11 is shown. The glenoid component 11 also has a single component plastic body 11A. The thickness of the plastic body 9B gradually increases from an anterior edge 11A to a posterior edge 11B thereof thereby creating a relatively smooth medial surface 11C from which a keel 12 extends. The design of this augmented glenoid component 11, however, suffers from at least the same drawbacks as the glenoid components 1 and 8.
Attempts to correct the four mentioned problems with posterior glenoid wear have included the invention of an augmented glenoid component with a step support face with the step support face being posterior. Such an augmented glenoid component is much more fully described in U.S. Pat. No. 6,699,289 to Iannotti et al issued Mar. 2, 2004. Hereby incorporated in its entirety by reference.
The augmented glenoid component of U.S. Pat. No. 6,699,289 requires a stepped pocket or locating surface for the augmented glenoid component. Such a stepped surface is very difficult to create. Certain processes for preparing the glenoid fossa for such a component can consist merely of hand or power tools, which are manually guided to prepare the cavity for receiving the augmented glenoid component.
What is needed therefore is a surgical procedure and instrumentation to overcome one or more of the afore mentioned problems.